The invention relates generally to systems and methods for interfacing multiple digital signal processing devices with a common bus, and more particularly to systems and methods for interfacing digital signal processing devices to an audio bus.
Multimedia computer systems are being developed which are compliant with Intel.RTM. Inc.'s AC 97 link (audio control) bus standard. With the increase in demand for audio applications, the AC link accommodates multiple streams of audio data so that multiple audio devices can be played and audio information may be available for processing. The AC link is a bi-directional, fixed rate serial pulse code modulated (PCM) digital bus. This bus, coming from a host central processing unit, contains multiple input and output audio data streams and communication data streams, such as modem data. The audio stream information may be any suitable number of audio streams such as that from a DVD player, a .WAV audio file, a television tuner, or any other suitable audio source. The AC link architecture, as known in the art, employs a frame based protocol which divides each frame into twelve outgoing and twelve incoming data streams. The data on the link also includes command information and synchronization pulses.
With audio information, there is typically a play and record mode indicating a transmit and receive audio stream. The audio information typically must be processed in real time to allow mixing and playing of audio streams in real time. This may be important when playing movies on the computer, mixing audio from computer games and other purposes. In addition, to facilitate modem communication, the AC link may also interface with one or more modem processors in addition to one or more audio digital signal processors, if desired.
A problem arises where multiple streams of audio must be processed in real time and modem communications are required at the same time. If a separate digital processing device was dedicated to each audio stream, the cost of the system may be prohibitive. Accordingly a single audio digital processor may afford cost savings. Likewise a single digital signal processor to handle the modem communication activities would also reduce costs. With such a system, however, it is important to minimize interrupts to the digital signal processing devices to avoid delays in real time processing and to avoid a reduction in system performance. Hence the maintenance of an acceptable throughput for audio processing and communication information is important. When having multiple digital signal processors on a same bus, with a limited bandwidth, it is desirable to have mechanisms which reduce the number of interrupts to the digital signal processing units. For example, if the baud rate of the modem is selectively increased, additional bandwidth from the link or bus is utilized by the communication digital signal processor thereby reducing the capability of the audio digital signal processor.
In addition, there exists a number of different audio protocols, such as I.sup.2 S, and other audio protocols that should be accommodated in an audio processing system to allow the system to interface to audio sources from differing suppliers. If different audio protocols are being transmitted over the same AC link, data can be lost without suitable accommodation.
Moreover, an AC link may have baud rates of approximately 12 MHz, whereas digital signal processing devices coupled to the AC link may process the audio information based on a clock speed of a much higher rate, such as 100 MHz. Since the digital signal processors are capable of much faster processing, communication over the link at an improper speed can also result in a loss of data. This can be catastrophic where real time audio processing is required. Conventional systems used to reduce the loss of data in such situations, typically use elastic storage elements such as dual port FIFO devices wherein one port is used for one clock domain and the other port is used for another clock domain. However, this can increase the cost of the system.
Accordingly, a need exists for a suitable audio bus interface system and method that facilitates reduction in DSP interrupts while affording protocol translation and eliminating the need for dual port FIFO configurations.